1. Field of the Invention
The present invention relates to a corrosion-resistant member.
2. Related Art Statement
Heretofore, in the processes of heating semiconductor wafers in semiconductor production apparatuses (for example, by PVD, CVD, diffusion, annealing, etc.), a sheet-by-sheet heating type system has been used wherein the wafers are treated one by one and a batch type heating system has been used, wherein a large number of wafers are treated simultaneously. As heating devices for the former system, use has been made of metallic heaters consisting of a heating resistive body, an insulating material, such as, mica covering the heating body, and a molding metal, such as, stainless steel, inconel, monel, etc., molding the insulating material; graphite heaters consisting of a heat-generating resistive graphite body and boron nitride covering and insulating the graphite body; and heaters of an infra-red radiation system utilizing condensation of light beam emanated from a halogen lamp. As heating devices for the latter system, a means has been adopted of heating a quartz or SiC tube accommodating the wafers by a surrounding heating resistive body.
Accompanying the recent increase of memory capacity of super LSI and progressive development of microprocessing, processes requiring a chemical reaction have been increased. Particularly, in semiconductor production apparatuses necessitating a super clean state, a halogen series corrosive gas, such as, chlorine series gases, or a fluorine series gas, etc., has been used for a deposition gas, an etching gas or a cleaning gas. In the heating systems of heating the wafers in contact with these corrosive gases, e.g. semiconductor production apparatuses, such as, thermal CVD devices, etc., a semiconductor-cleaning gas consisting of halogen series corrosive gas, such as, ClF.sub.3, NF.sub.4, CF.sub.4, HF, or HCl, etc., is used after the deposition stage. In the deposition stage also, a halogen series corrosive gas, such as, WF.sub.6, SiH.sub.2 Cl.sub.2, or monosilane, etc., is used as a deposition gas.
Next, cleaning gases nowadays used in thermal CVD devices, etc., are illustrated in the following Table 1.
TABLE 1 ______________________________________ Cleaning gas Item CF.sub.4 NF.sub.3 ClF.sub.3 ______________________________________ Etching Rate slow ordinary quick Requirement for plasma yes yes no Reactivity at room no no yes temperature Object for etching Poly-Si W SiN,TiN,BN ______________________________________
Among the cleaning gases shown in the above Table 1, ClF.sub.3 has been found to react with a metal at room temperature to form a metal fluoride resulting in corrosion of the metal.
Moreover, corrosion is formed at around 120.degree. C. or a temperature of not less than 300.degree. C., respectively, when stainless steel or inconel is used as the above-mentioned metallic heater, which corrosion forms particles and becomes a cause of deficiency of the semiconductor. Also, boron nitride or silicon carbide is gasified when exposed to a high temperature cleaning gas, and hence becomes a cause of defects of semiconductors due to influence of contamination. Also, when a metallic heater is used in a CVD device, etc., the chamber of the CVD device becomes a high vacuum of 10.sup.-4 Torr at the maximum, so that an efficient heating of wafers is very difficult if a metal of low heat radiation is used and a very long time is required for heating the wafers. Also, a quartz tube has a problem of its devitrification resulting in decrease of the strength thereof.
In order to avoid such problems of corrosion, semiconductor wafers have to be heated to a high temperature for subjecting a film-forming treatment, etc., and thereafter the heater temperature has to be lowered to not more than 300.degree. C. or not more than 100.degree. C. and the above cleaning gas has to be blown to the heater or the like high temperature member to clean the same at such a condition that the film which has to be removed reacts with the cleaning gas but the high temperature member including the heater do not react with the gas. Therefore, a considerably excessive time is required for the cycle of elevation and lowering of the temperature and throughput of the semiconductor at the time of producing the same is decreased. Even when a carbon heater is used for the heating, corrosion occurs at a temperature of higher than room temperature by 150.degree. C. or more to form a powder on the heater surface resulting in formation of particles.
Furthermore, when a halogen series corrosive gas is used as a deposition gas, deposition is effected at a high temperature of 300.degree.-1,100.degree. C., for example, so that the above problem of corrosion can not be avoided.
The inventors studied utilization of a silicon nitride sintered body having a high thermal shock resistant property as a substrate of susceptor or ceramic heater for a semiconductor production apparatus. However, upon further study we have found out that the silicon nitride sintered body is easily corroded by the cleaning gas or the etching gas for the semiconductors.